This invention relates to a gas release (venting) method in a metal mold comprising two split mold half portions which have opposite inner surfaces to define a release path for gases along which a charge of molten metal is advanced.
In a metal mold, generally, when a charge of molten metal at an elevated temperature (about 600.degree. C. in case of die casting) is passed through the gas release path defined in the mold carried by the gas escaping the mold as it is filling, the molten metal immediately effects heat-exchange with the inner surface of the path upon contacting the path inner surface and the heat of the molten metal is lost to the metal mold and as a result, a thin layer of solidified metal is formed on the entire inner surface of the gas release path and the thus formed solidified metal layer which closely adheres to the path inner surface in such a manner that the layer can not be easily separated from the path inner surface and remains to cover the entire inner surface.
Even when such a layer of solidified metal has a small thickness, the film substantially hinders the transfer of heat from the molten metal to reduce the heat transfer efficiency to the degree that the cooling and solidification of the molten metal is detered. This makes it difficult to substantially increase the cross-section area of the gas release path and to reduce the distance of the path in the flow direction of the molten metal.